• Journal of Biomedical Engineering Research
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• v.16 no.4
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• pp.431-438
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• 1995

Functional imaging based on the susceptibility only is achieved by separation of the susceptibility effect from the mixture of flow effect by use of a tailored RF pulse in conjunction with gradient echo sequence. Using the tailored RF pulse the susceptibility enhanced functional imaging appears to be explicitly related to the deoxygenation processes, while in the conventional gradient echo technique functional contrast on $T2^{*}$ effect images appear to be mixed with a significant fraction of blood flow (in- flow) signals of both arterial as well as venous bloods due to the nature of the fast sequence employed with the gradient echo technique. In this paper, using the tailored RF pulses, one can unambiguously separate the susceptibility and flow effects in functional imaging. Since the signal obtained can be made sufficiently high and represents oxygenation process more accurately, it seems possible to study quantitative oxygen metabolisms in brain function hitherto difficult to do with other gradient echo techniques.

• Smart Media Journal
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• v.11 no.1
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• pp.46-57
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• 2022

In this paper, multi-region based Radial Graph Convolutional Network (MRGCN) algorithm which can perform end-to-end action recognition using the optical flow and gradient of input image is described. Because this method does not use information of skeleton that is difficult to acquire and complicated to estimate, it can be used in general CCTV environment in which only video camera is used. The novelty of MRGCN is that it expresses the optical flow and gradient of the input image as directional histograms and then converts it into six feature vectors to reduce the amount of computational load and uses a newly developed radial type network model to hierarchically propagate the deformation and shape change of the human body in spatio-temporal space. Another important feature is that the data input areas are arranged being overlapped each other, so that information is not spatially disconnected among input nodes. As a result of performing MRGCN's action recognition performance evaluation experiment for 30 actions, it was possible to obtain Top-1 accuracy of 84.78%, which is superior to the existing GCN-based action recognition method using skeleton data as an input.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.59-66
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• 2012

The purpose of this study is to estimate the behavior and the mechanism of debris flow on the slope, which has specially various gradient plane. The numerical simulation was performed by using the Finite Differential Element method (FDM) based on the equation for the mass conservation and momentum conservation. The mechanism of flow type for debris flow is divided into three flow types which are stony debris flow, immature debris flow, and turbulent water flow, respectively. First, flow discharge, water flow depth, sediment volume concentration was investigated by variable input of flow discharge at the straight slope angle and two step inclined plane. As the input of flow discharge was decrease, flow discharge and water flow depth was increased, after the first coming debris flow only reached at the downstream. As the input of flow discharge was increased, the curve of flow discharge and flow depth was highly fluctuated. As the results of RMS ratio, the flow discharge and flow depth was lower two step slope angle than the straight slope angle. Second, the behavior of debris flow was investigated by the four cases of gradient degree at the downstream of slope angle. The band width of flow discharge and flow depth for $14^{\circ}$ between $16^{\circ}$ was higher than other gradient degree, and fluctuation curve was continuously high after 10 seconds.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.1042-1048
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• 2005

Numerical investigation has been made on the stent design to minimize the neointimal hyperplasia. Computational fluid dynamics is applied to investigate the flow distributions in the immediate vicinity of the given idealized stent implanted in the blood vessel. Parametric study on the variations of the number of stouts, stent diameters, stent spacings and Reynolds numbers has been conducted using axi-symmetric Navier-Stokes equations. An initial difficulty in the study is to determine the optimal stent design to understand the flow physics of the flow disturbance induced by stent. The size of recirculation zone around stent is depend on the stent diameter, number of stent wire and Reynolds number but is insensitive to the stent wire spacing. It is also found that when the flow is in acceleration, the flow sees a more favorable pressure gradient, and the separation zones are smaller than the steady flow case. When the flow is in deceleration and the flow sees a more adverse pressure gradient so that the separation zones are larger.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1731-1740
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• 1995

Experimental investigations have been made to study the double-diffusive nature of convection of an initially stratified salt-water solution due to heating from below in a rotating cylindrical cavity. The objective is to examine the flow phenomena and the heat transfer characteristics according to the changes in temperature gradient, concentration gradient and rotating velocity of cavity. Thermal and solutal boundary conditions at side wall are adiabatic and impermeable, respectively. The top and bottom plate are maintained each at constant temperature and concentration. The cavity is put into a state of solid body rotation. Like the stationary case, the types of initially-formed flow pattern are classified into three regimes depending on the effective Rayleigh number and Taylor number; stagnant flow regime, single mixed-layer flow regime and successively formed multi-mixed layer flow regime. At the same effective Rayleigh number, the number of initially-formed mixed layer and its growth rate decrease as the effect of rotation increases. The temperature and concentration profiles are both uniform in each layer due to convective mixing in the layered-flow regime, but look both liner in stagnant flow regime and single mixed-layer flow regime. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly.

• Journal of the Korean Society of Tobacco Science
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• v.18 no.1
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• pp.92-99
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• 1996

A mathematical model of the pressure gradient of supercritical CO2 in a vertical tobacco bed was developed in this study. In particular, the compaction of the tobacco as a function of temperature and CO2 flow is included in the model. Downflow of CO2 (low condition is described. At velocities in excess of 0.6 cm/sec at 7$0^{\circ}C$, there is a large increase in pressure gradient for beds deeper than about 0.5 m. The proposed model offers a better understanding of operating the process using supercritical CO2.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.668-676
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• 1991

Turbulent flows around tube banks and in the diffuser were studied using a non-orthogonal boundary fitted coordinate system and the modified K-.epsilon. turbulence model. In these cases, many problems emerge which stem from the geometrical complexity of the flow domain and the physical complexity of turbulent flow itself. To treat the complex geometry, governing equations were reformulated in a non-orthogonal coordinate system with Cartesian velocity components and discretised by the finite volume method with a non-staggered variable arrangement. The modified K-.epsilon. model of Hanjalic and Launer was applied to solve above two cases under the condition of strong and mild pressure gradient. The results using the modified K-.epsilon. model results in both test cases.

• Journal of Powder Materials
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• v.10 no.6
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• pp.448-455
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• 2003

$TiO_2$ nanopowder has been synthesized by means of the flame method using a precursor of titanium tetraisopropoxide (TTIP, Ti$(OC_3H_7)_4)$. In order to clarify the effect of cooling rate of hot flame on the formation of $TiO_2$ crystalline phases, the flame was controlled by varying the mixing ratio and the flow rate of gases. Anatase phase was predominantly synthesized under the condition having the steep cooling gradient in flame, while a slow cooling gradient enabled to form almost rutile $TiO_2$ nanopowder of above 95%.

• Journal of Welding and Joining
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• v.17 no.6
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• pp.70-77
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• 1999

Surface depression in the arc welding is calculated numerically to analyze its influence on pool convection and oscillation. The magnitude of surface depression due to arc pressure on the stationary GTA pool surface is relatively small, and fluctuations of the surface and velocity are caused mainly by arc pressure. The inward flow on the surface due to the electromagnetic force and positive surface tension gradient acts to decrease surface depression. Surface depression appears to have minor effects on average flow velocity and thus pool geometry. Pool oscillation occurs due to surface vibration, and oscillation frequencies are affected mainly by the surface tension and pool width. The input parameters such as arc pressure and current have negligible effects on the oscillation frequency, and the surface tension gradient has limited effects. Since the oscillation frequency varies slightly according to penetration, pool oscillation for the partial penetration weld pool is applicable to monitor the pool width.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10d
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• pp.478-480
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• 2002

영상 분할은 임상에서의 진단과 분석 및 3차원 가시화를 위해 선행되어야 할 필수 과정이다. 의료영상은 영상이 가지는 데이터 자체의 고유한 제약들과 해부학적 변이성 때문에 영상분할에 어려움이 있다. 본 논문에서는 의료영상의 분할을 위해 스네이크의 새로운 외부 힘으로 Gradient Vector Flow(GVF)를 이용한 방법을 제안한다. 제안된 방법은 2차원 의료영상에서 에지 맵(edge map)을 구하고, GVF을 계산하여 스네이크의 경계선과 같이 관심 있는 특징의 에너지 함수가 최소가 되는 GVF 스네이크(snake)를 구한다. 제안된 방법을 초음파영상과 자기공명영상 같은 의료영상의 분할에 적용한 결과 기존의 스네이크와 달리 잡음이나 오목한 부분이 있는 객체들을 성공적으로 분할하였다.